Artificial glass



?atenied elune l, @438 lin Strain, Akron, and William A. Prairie, Ear berton, @hio, assignors to Pittsburgh lPlate Glass Company, Aileghe poration of Pennsylvania ny (County, Pa, a cor- No Drawing. Application February 8, 19%, Serial No. 317,833

@laims.

This invention relates to an artificial glass and to the manufacture of such a material. In the past, numerous attempts have been made to develop a product possessing the characteristics of transparency, hardness, and temperature, solvent and wear resistance, corresponding to that of glass and exhibiting greater flexibility and resistance to shattering than glass.

Numerous materials have been proposed for this purpose but prior to the present invention, no product has been developed which possessed all of these desirable characteristics. The wellknown methyl methacrylate polymer, which has been developed in recent years, has been one of the most successful resins yet introduced as a glass substitute. However, these materials are undesirably soft and are readily scratched. Thus, in many cases, where they are used in lieu of glass, they cannot be cleaned conveniently for the reason that the surfaces thereof become seriously abraded during wiping or scrubbing operations. In addition, the surfaces of these plastics are attacked by Water or organic solvents. The impairment of the surface often occurs during the use of these materials which has seriously limited the extent of their use as an artificial glass. Similar objections have been raised against most of the thermoplastic resins which have been suggested as glass substitutes.

In accordance with our invention, we have been. able to provide a composite resinous product of high transparency and stability to light which is resistant to the action of abrasives, organic solvents and which also possesses the properties of great flexibility and resistance to shattering. More particularly we have discovered that products of high flexibility, wear and scratch resistance may be secured by providing a relatively soft resinous base with a relatively harder surface or coating on one or all sides thereof. Such surfaces may be secured by providing the base with a film, coating or layer of the harder resin which is generally of the thermosetting type such as may be derived from the polymerization of an organic compound containing two or more polymerizable groups. This compound may be applied, for example, in its monomeric or partially or intermediately polymerized form and subsequently completely polymerized to the required degree. If desired, the polymer to be surfaced may be partially impregnated or soaked with the coating agent in its monomeric or partially polymerized or intermediately polymerized state in order that the base polymer may be permeated with the agent whereby a more firm bond between the base and the hard surface coating or layer is obtained.

We have been able to increase the abrasion and solvent resistance of relatively soft resins or plastics to a surprising degree. In accordance with this invention it is preferred to use as the base material a flexible resinous product which is transparent, resistant to shattering, and possesses some degree of elasticity. Various poly mers of saturated esters or amides of acrylic or cz-SllbStitllti-Zd acrylic acids, such as polymerized methyl methacrylate, ethyl methacryiate, methyl methacrylamide, methyl or ethyl acrylate, methyl or ethyl chloroacrylate, or the higher esters of; these acids such as the propyl, butyl, isobutyl, phenyl or stearyl esters thereof, or the corresponding monoesters of polyhydric alcohols, such as ethylene glycol monomethacrylate, glycerol methacrylate or mixtures of these polymers have been found suitable for base materials. Other thermoplastic polymers which are sufficiently flexible, transparent and stable to light or heat to permit their use in' lieu of glass also may be coated or surfaced in accordance with our in vention to provide them with hard, durable, sol-- vent-resistant and transparent surfaces. For example, various vinyl polymers, such as polyvinyl acetate, polyvinyl chloride, polyviny] but/yrate, polystyrene, polyvinyl butyral, polyvinyl benzoate, or other fusible or other thermoplastic polyvinyl halide or ester of saturated aliphatic or araliphatic acid may be used as base materials. In similar manner, the corresponding allyl or methallyl polymers or other polymer of unsaturated alcohols or esters or ethers thereof such as polyallyl acetate, polyallyl benzoate, polyallyl butyrate, etc. may be used.

As a further modification it is found that flexibie resinous plastics of the thermosetting type which are substantially insoluble end/or infusicle and are resistant to shattering may be coated or surfaced in accordance with the present invention. Thus, polymers such as may be prepared by the polymerization of polymerizable materials containing in the monomeric form two or more polymerizable groups in which one group may be CH=Z and the other may be th same or another polymerizable olefinic double bond or triple bond which are separated by at least one atom so that the double bonds do not form a conjugated system or other polymerizable group may be polymerized in the presence of plasticizers or such materials may be polymerized with other polymerizable materials which are capable of forming linear compounds such as the polymerizable compounds containing the group for example, acrylic, methacrylic, chloracrylic, or other alpha-substituted acrylic acid or crotonlc acid and an unsaturated alcohol such as allyl methacrylate, chloracrylate, methacrylate, etc. or the corresponding Z-chlorallyl, crotyl, methallyl, ethyl ally], oleyl, propargyl, furfuryl, etc. esters or other unsaturated compounds containing two or more polymerizable groups such as allyl, methallyl, crotyl, etc., propiolate, or the polyallyl, polymethallyl, polycrotyl, polychlorallyl, polyethyl allyl, etc. esters such as diallyl, dimethallyl, diethylallyl, dicrotyl, ell-2- chlorallyl, dioleyl, esters of polybasic acids such as oxalic, maleic, fumaric, tartaric, malonic, phthalic, carbonic acids, etc., or the corresponding dior tri-esters of phosphoric, silicic, titanic, adipic, succinic, or citric acids, or other poly esters of unsaturated alcohols and polybasic acids or monoesters of unsaturated acids such as mono allyl maleate, mono crotyl maleate, or mixed esters such as allyl crotyl maleate, phthalate, malonate, tartrate, etc. may be copolymerized with compounds capable of forming linear polymers. Suitable compounds Polymerizing to form the so-called linear polymer which may be used for polymerization in accordance with the present invention are vinyl or allyl polymers such as vinyl chloride, styrene, vinyl propionate, vinylidene chloride, vinyl acetate, allyl benzoate, allyl acetate, mono allyl phthalate, allyl methyl phthalate, polymers of methallyl, chlorallyl, crotyl, ethyl allyl or oleyl alcohol or esters or ethers thereof, or other compounds capable of polymerizing to form a polymer of an unsaturated alcohol or ester, or ether thereof, or a polymer of an unsaturated acid or ester, or amide thereof, such as polymers of saturated esters of acrylic, chloracrylic or methacrylic acid or cnotonic acid, for example, methyl, ethyl, propyl, butyl, amyl, lauryl, or stearyl acrylate, methacrylate, chloracrylate, or crotonate. Similar polymers may be secured by polymerizing unsaturated polyesters o1 polyhydric alcohols such as glycol, glycerol, mannitol, di, trl, or poly acrylate, methacrylate, crotonate, chloracrylate, etc. Copolymers which may be suitable for use as the base plastic in accordance with the present invention have been described in United States Patents granted to Benjamin Garvey, Nos. 2,155,590, and 2,155,591, and also to United States Patents Nos. 2,160,931, 2,160,932, 2,160,940, 2,160,941, 2,160,942, and 2,160,943.

In similar manner, polymers of varying hardness may be obtained by polymerizing the above agents in the presence of a quantity, generally from to 70 percent, of a compatible plasticizer, such as dibutyl phthalate, or other phthalates such as ethyl, propyl, isopropyl, butyl, isobutyl, cyclohexyl butyl, phthalates; phosphates, such as tricresyl phosphate, esters of polyhydric alcohols, such as the glycol or glycerol esters, tributyrin, triacetin, glycol benzoate, or substituted imides, such as tetracthyl phthalamide, or other hydrocarbons such as alkyl naphthalene, amyl naphthalene, dixylyl ethane, etc. In this manner it is possible to produce products which possess great flexibility. Similarly, numerous materials such as oleyl methacrylate, oleyl chloracrylate, etc. which may be polymerized alone to form flexible products without plasticizers may be used as base materials.

Most efllcient results have been secured by use of a coating of a polymer of the unsaturated esters of acrylic and lat-substituted acrylic acids or the polyhydric alcohol polyesters of these acids or the corresponding amides thereof, such as allyl acrylate, allyl methacrylate, allyl chloracrylate, methallyl acrylate, methallyl methacrylate, methallyl chloracrylate, ethyl allyl methacrylate, crotyl methacrylate, z chlorallyl acrylate, 2-chlorallyl methacrylate, propargyl methacrylate, acrylate, or chloracrylate, oleyl methacrylate, vinyl acrylate, vinyl methacrylate, resorcinol dimethacrylate, glycol dlmethacrylate, glycol thacrylate, glycerol diacrylate, glycerol dior trimethacrylate or mixtures thereof, glycol diu-chloracrylate, glycerol dior tril a-chloracrylate, or polyglycol diacrylate, glycerol dior triacrylate or the acrylic, methacryllc, or a-ChlOl'fiClYllC esters of higher polyhydric alcohols, such as sorbitol or mannitol, wherein at least two of the hydroxyl groups are esterified with the above named acids. Additionally, hard solvent-resistant coatings may be secured through use of the corresponding amides of the polymerizable unsaturated acids, such as vinyl, allyl, methallyl, ethylallyl, or oleyl acrylamides, methacrylamides, or chloracrylamides. In addition, other materials containing polymerizable groups CH1=(E or other polymerizable groups of this type, such as vinyl allyl ether, divinyl ketone, diallyl crotonamide, diallyl methacrylamide, diallyl acrylamide, monoallyl methacrylamide, allyl styrene, or substituted urea derivatives, such as diallyl urea, etc. may also be used.

Other products may be secured by polymeriza-- tion 01' other organic compounds which contain at least two polymerizable groups preferably those in which one of the groups i the polymerizable group Okt- and is separated by at least one atom whereby the groups are unconiugated. For example, unsaturated aliphetic esters of unsaturated aliphatic acids, such as the unsaturated crotonate esters, allyl crotonate, crotyl crotonate, methallyl crotonate, oleyl crotonate, z-chlorallyl crotonate, ethylallyl crotonate, or other unsaturated esters, such as allyl oleate, allyl itaconate, ally] propiolate, diallyl maleate, ally] ethyl maleate, dimethallyl maleate, ethyl methallyl maleate, methyl allyl maleate, vinyl allyl maleate, divinyl maleate, dipropargyl maleate, i'umarate, ltaconate, succinate, etc., or other mono or polyester formed by esteriflcation or maleic or iumaric acid or their substituted derivatives with an unsaturated alcohol or allyl citraconate, allyl fumarate, methallyl iumarate, oleyl i'umarate, allyl cinnamate, or the corresponding methallyl, ethylallyl, propargyl, or crotyl esters thereof, or the unsaturated polyesters of saturated polybasic acids and unsaturated monohydric alcohols such as diallyl oxalate, diallyl malonate, di-or triallyl citrate, diallyl tartrate, diallyl phthalate, diallyl carbonate, etc., or the corresponding methallyl,

propargyl, or crotyl esters thereof may be used for this purpose. Similarly, the polyesters of polyhydric alcohols and monobasic unsaturated acids such as ethylene glycol dicrotonate, g ycerol dior tricrotonate, glycol dicinnamate, glycerol dicinnamate, glycerol diproplolate. lycol dipropiolate, or the corresponding esters of other glycols such as the propylene glyools, butylene glycols, or polyglycols thereof or the higher alcohols such as sorbitol or mannitol, etc. may be polymerized in this manner. Other organic oxygen compounds which contain at least two polymerizable double bonds and are capable of polymerizing to a final form which is transparent,

hard and substantially infusible and insolublemay be used. Thus, unsaturated polyethers of polyhydric alcohols, such as the diallyl, -methallyl, -oleyl, or -crotyl ethers of glycols, such as ethylene, propylene, or butylene glycol or polyglycols such as diethylene glycol, tetraethylene .glycol, etc. or the dior triallyl methallyl, oleyl,

or crotyl ethers of glycerol or the corresponding polyethers of the higher polyhydric alcohols, such as mannitol or sorbitol may be applied and polymerized in accordance with our invention.

In addition, esters of inorganic acids such as diallyl sulphate, dior triallyl phosphate, dior triallyl borate, dior triallyl phosphite, allyl silicates, allyl titanates, or similar esters may be polymerized by our p ocess.

In order that a product of maximum surface hardness be produced, it is preferable to make use of compounds wherein the number of carbon atoms in the molecule of the monomeric form is not excessive. Thus, a methacrylate polymer which is surfaced with polymeric allyl or methallyl methacrylate or chloracrylate exhibits a greater resistance to wear and is harder than a similar polymer which is surfaced with polymerlc oleyl methacrylate.

The trend toward softer product as the number of carbon atoms increase may be minimized by increasing the number of polymerizable double bonds in the composition. Thus, sorbitol hexamethacrylate polymerizes to form a product which exhibits greater hardness than does polymeric oleyl methacrylate. In general, it is preferred to make use of agents wherein the ratio of the number of carbon atoms to the number of polymerizable olefinic groups does not exceed and preferably materials wherein the ratio does not exceed 8 are made use-of. In addition, it is found that most desirable products are secured through use of materials containing not in excess of 10 carbon atoms, in each of the alcohol residues and the acid residues. The softer polymers may be used as base materials.

The plastic base may be surfaced in any convenient manner which permits the production of a hard surface which is free from visible surface defects. Production of such a film by application of the monomer often is found to be exceedingly dimcult. This is particularly true of actively polymerizable materials such a glycol dimethacrylate, glycerol trimethacrylate, allyl methacrylate, allyl acrylate, etc., since when such agents are applied to a base in monomeric or as syrupy solution and polymerized, cracked or irregularly surfaced products generally are obtained.

It has been found that these difllculties may be largely eliminated, however, by dissolving a -quantity, generally in excess of 10 percent of a fusible heat-convertible polymer such as a fusible heat-convertible polymer of glycol or glycerol methacrylate or similar polymerizable material and applying the mixture to the base. It has been found that the application of the coating may be most eiiectively controlled by applying the surfacing agent in its intermediate, fusible, polymeric stage to the thermoplastic base and completing the polymerization. It has been discovered that polymerizable compounds, such as those which are contemplated herein and which ordinarily polymerize to form infusible, insoluble products, may, under proper conditions, be polymerized to form a soluble, thermoplastic polymer which may be polymerized further to the infusible state.

A fusible polymer of this type may be prepared, for example, by conducting the polymerization in a solution which is capable of dissolving the polymer and interrupting polymerization at the proper time. Thus. when a polymerizable compound containing two or more polymerizable groups, such as allyl chioracrylate, allyl methacrylate, etc., is dissolved in a solvent such as acetone, dioxane, chloroform, etc., a soluble polymer is initially formed, but as polymerization proceeds, the insoluble polymer is produced and the solution is converted into a non-reversible gel. By interrupting polymerization before the gel is formed, a soluble, fusible polymer may be secured. This polymer is found to be soluble in a majority of the solvents in which the polymer of the saturated acrylate or vinyl esters are normally soluble. Acetone chloroform, toluene, dioxane, triacetin, phenyl cellosolve, ethyl cellosolve acetate, benzene, etc. are suitable solvents, in general. The fusible polymers may be recovered by evaporation or distillation of the solvent by addition of a non-solvent, such as methyl, or ethyl alcohol, or Water.

In accordance with one effective method of interrupting polymerization, inhibitors, such as pyrogallol, hydroquinone, aniline, phenylene diamine, sulphur, thiophenol, organic or inorganic salts or complexes of the reduced formsof metals, such as copper, manganese, cobalt, nickel, etc., dipentene, etc., may be added to the polymer during polymerization or before polymerization has been initiated. These solutions may be treated to remove the solvent by slow evaporation, treatment with a non-solvent, or by other suitable method and fusible thermoplastic polymers which may be molded, machined, cut, bent or otherwise worked into desirable form thereby attained. During shaping or after final shaping, the products may be completely hardened and rendered infusible by suitable methods hereinafter more fully set forth.

In the polymerization of allyl and methallyi esters of acrylic and alpha-substituted acrylic acid, such as allyl methacrylate, it has been found that the yields of fusible polymer appears to be dependent to a great extent upon the concentration of the monomer in the solution undergoing polymerization. Thus, when very concentrated solutions containing a large quantity, for example, in excess of 40-50 percent, of the monomeric allyl or methallyl methacrylate, are subjected to conditions of polymerization, the amount of fusible polymer which may be secured prior to gel formation is very. low, often not in excess of 5 percent by weight of the theoretical yield. Conversely, when solutions containing somewhat lower concentrations of monomer, for

4 example up to 30 percent by weight, yields of the fusible polymer upward of 95 percent of thetheoretical may be secured. Accordingly, it is preferred to deal with solutions having 2. monomer concentration below 40 percent by weight.

The yield of fusible polymer appears to be increased by treating the solutions at increased temperatures and increased catalyst concentrations. Thus, substantially greater yields may be secured by polymerizing allyl methacrylate solutions at 100 C. or above, than may be secured at 60 C. Catalyst concentrations up to 5 percent or more may be used in some cases. In general, conditions favoring the formation of lower molecular weight polymers appear to result in increased yields of fusible products. Further details relating to the preparation of a fusible glycol acrylate or similar polymer may be found in copending application of Franklin Strain, Serial No. 257,133, filed February 18, 1939.

In many cases, the fusible polymer may be obtained by conducting the polymerization in the substantial absence of solvents. This is particularly true in the production of fusible polymers from those materials which polymerize slowly, for

example, the unsaturated crotonic acid esters, such as allyl or methallyl crotonate, or the corresponding phthalates, maleates, axalates, itaconates, etc. In some cases it is found desirable sence of solvents and subsequently to recover the I fusible polymer by dissolving the product in a suitable solvent such as acetone and precipitating the fusible material with a nonsolvent such as water or methyl alcohol. In many cases, however, the

residual monomer may be removed by distilla- :3

tion at low temperatures in a vacuum. This process is particularly effective in dealing with materials which polymerize to form viscous products which retain a substantial quantity of unpolymerized monomer.

By operation in accordance with this modification, the base is coated with a composition containing both monomer and polymer as polymerizable constituents. In such a case, however, it is generally desirable that the intermediate fusible polymer be present in an amount in excess of that which can be obtained under normal circumstances by partially polymerizing, undissolved, or undiluted monomer. Generally speaking, the fusible polymer should comprise a major portion of the polymerizable constituents in the coating composition. For the more active materials such as allyl, methallyl, ethyl allyl, or chlorallyl acrylate, methacrylate, or chlorocrylate, or the corresponding polyhydric alcohol polyesters, the fusible polymer content should be above percent by weight of the polymerizable constituents. For less active products, such as diallyl phthalate, or diallyl maleate, the fusible polymer content should be above percent and preferably above 50 percent or more of the polymerizable constitutents in thecoating composition.

In coating thermoplastic bases, such as polymers derived from methyl methacrylate, with the fusible convertible polymer, the polyuner is generally applied as a solution which is allowed to evaporate to form a film. The fusible polymers of the type herein described are soluble in the solvents which are generally used for other fusible vinyl polymers, such as acetone, carbon tetrachloride, trichloro ethylene tetrachloroethylene, xylene, toluene, benzene, dioxane, chloroform, triacetin, phenol cellosolve, etc. dried, the product may be subjected to polymerization conditions in order to convert the surface iii After the film has film to the infusible state. Pressure is applied to the film in order to promote adhesion and impart smoothness to the surface. This may be done for example, by pressing the coated product between smooth plates, for example, smooth glass plates, during curing of the coated sheet. This process is generally termed press polishing in the art and the surfaces thereby produced are known as press polished surfaces.

In order to insure the production of a transparent sheet which is free from surface defects and which possesses a coating having optimum adhesion, it is preferred that the infusible polymer be present as a very thin film. Preferably. this film should be of such thinness that a pressure which is just sufficient to cause the base plastic to yield will also cause the film to yield in a corresponding manner without fracture or impairment of the film. In applying films, such as allyl methacrylate, etc., to polymethyl methacrylate, it is found that optimum results may be secured by application of not substantially in excess of 20 grams of the coating material per sq. ft, of methacrylate surface to be coated. The films thus produced are below about 0.01 inch in thickness, being in general, about 0.0003 inch thick, in most cases. Where allyl methacrylate or similar agent is used as the coating, the films preferably are less than 0.002 inch in thickness. It is to be understood, however, that the critical thickness for maximum hardness and adhesion varies with the composition of the plastic base, plasticizers used therein, flexibility thereof, etc., and that products having substantially greater thickness may be produced, if desired.

By use of a film of such thinness, it is possible to obtain a product of unusual scratch resistance. To a large degree, this is due to the higher flexibility of thin films and to the fact that the flexible thin films when in close adherence to the base plastic possess great resiliency and elasticity and resist penetration. The polymers derived from allyl methacrylate and similar materials are not only harder than polymers of methyl methacrylate but also are somewhat more rigid and brittle. Thus, where the film is relatively thick, a stress applied at some point on the .surface thereof is not transmitted to the plastic below the film at any single point. In consequence, when a weighted point is drawn across such a thick film, the film itself takes up most of the weight of the point and the scratch resistance of the surface thereof is merely the scratch resistance of In contrast, when a weighted point is drawn across the surface of a coated plastic having a thin film of the surfacing polymer, both the base polymer and the surface polymer cooperate in resisting deformation under the point, some of the stress being transmitted to each. Since the film is thin, it is sufficiently flexible to conform to small deformation of the base without fracture and since it resists penetration, scratching by the weighted point is thereby avoided.

Stress applied to a localized portion of such a coated sheet may result in a transient yielding of the surface thereof, but upon release of the applied stress, the base by reason of its elasticity, returns to its original form and since the film remains unfractured and unpenetrated, the coated product remains unscratched and undeformed. In general, the thin films used in accordance with this invention are not fractured until the base is deformed to a visible, substan-. tially permanent degree. In many cases the coated sheets have been bent to an angle of or more degrees without apparent fracture or impairment of the film.

In some cases, difllculty may be encountered in securing a coating which is sufficiently adherent and free from fracture or other surface defects for commercial use. Difficulties of this nature are often encountered in applying unsaturated acrylates, such as allyl methacrylate to cellulose thermoplastics, such as cellulose acetate. In such a case, it may be desirable to provide the thermoplastic with an intermediate coating of a more mutually compatible composition, such as a coating of cellulose nitrate.

The products produced in accordance with this invention are unusually hard and possess the transparency of the plastic base. The resistance to abrasion and scratch of these materials approximates the abrasion and scratch resistance of glass.

Certain tests indicate a resistance to scratch which is ever superior to glass. Thus, in accordance with one test a rounded diamond point, normally used in a glass cutting pencil, was mounted to move freely in a vertical direction upon a rocker arm and used to compare the scratch resistance of the present product with that of uncoated resins and of glass. In accordance with this test, progressively increasing weights were placed upon the diamond point, the point placed upon a sheet of the product to be tested and the sheet moved in a straight line to] permit the point to form a scratch upon the s ee The following table illustrates the loads reguigd to produce a scratch upon the products es d:

It will be evident that the above results are merely comparative and vary considerably in accordance with the sharpness of the diamond point. Obviously, a finely ground diamond point scratches all materials because of its extreme hardness. However, the above tests clearly demonstrate the superiority of applicant's product over other resinous products.

In many cases precautions must be taken in order to produce a surface which exhibits high resistance to scratch. Thus, it is found that upon application of a xylene solution of the fusible polymer to the surface of methyl methacrylate polymer and polymerization of the polymer without application of pressure between plates, the film thus obtained often has no appreciably improved resistance to scratch. Upon further curing of the coated material, in contact with a solid surface or a liquid surface such as vegetable or mineral oil, mercury, wax, etc., at a suitable temperature, for example, 100175 C. with pressure, the film is converted to the normal scratch resistant state. The exact cause of this phenomenon is not known at present but is believed .to be due to the presence of a small quantity of residual solvent or incompletely polymerized material which tends to soften the film. This belief appears to be warranted by the fact that when films are cured between plates with more or less pressure, a small residue or exudation remains upon the surface of the plates.

When scratched products are examined under the microscope there is observed a marked difference in the type of scratch of a film which has been freed of solvent or otherwise treated to form a surface film having a scratch resistance substantially greater than that of the base and films wherein the scratch resistance has not been developed. Thus, when a completely cured film, having high scratch resistance is subjected to the scratch test referred to above under a weight which is just sufiicient to scratch the film the scratch produced, when examined under a microscope of 30 magnification, is characterized by the presence of a series of closely spaced, substantially parallel lines intersecting the path of the point and indicating a plurality of cross fractures of the film. Since this type of scratch is apparently due to the highly elastic character of the surface we have designated this characteristic type of scratch as elastic scratch. In contrast, incompletely hardened surfaces so tested form scratches which are entirelydifferent. Such scratches consist merely of a line delineating the path of the point without the cross fractures observed in the former product. Such a scratch indicates deformation as distinguished from cross fracture of the film and for purposes of convenience may be termed a plastic scratch. Bases coated with. films exhibiting this plastic scratch possess a scratch resistance only slightly higher than that of the base itself while bases coated with films exhibiting the cross fractured type of scratch are substantially more scratch resistant than the base.

The following examples are illustrative:

Example I.A mixture of '15 parts by weight of benzoyl peroxide, 225 parts by weight of monomeric allyl methacrylate and 1275 parts by weight of acetone was refluxed at 63 C. for three hours. 2800 parts by weight of methyl alcohol was then added to the mixture. The resulting mixture was then poured, with stirring, into 1000 parts by weight of a methyl alcohol-water mixture containing per cent of methyl alcohol by volume. The precipitate thus formed was coagulated and recovered from solution.

A sheet of commercial molded Lucite which is a commercially available polymer or methyl methacrylate was pressed between smooth plates in order to render the surface more homogeneous and smooth. A xylene solution containing 5.5 grams of polymer per cc. of solution was poured and spread evenly over the surface of the pressed plastic. 14.4 cc. of solution was applied per square foot of surface and the coated product was air-dried for 35 minutes. The Lucite sheet was then coated on the opposite side in the same manner and was then pressed between glass plates at a pressure of 1000 lbs. per sq. in. and at a. temperature of C. for 40 minutes. The coated sheet thus produced was colorless, transparent, and free from surface defects. In order to compare its scratch resistance with glass, a diamond point pencil weighted with varying weights was applied to sheets of glass and the coated Lucite prepared in accordance with this sample. It was observed that heavier weights were required to produce visible scratches onthe coated Lucite" than were required to produce such scratches on glass.

pressure of 6 mm. of mercury.

The abrasion resistance of the coated product to falling 4060 mesh silica sand, using the apparatus described in Physical and Chemical Examination of Paints, varnishes, Lacquers and Color by Gardner, 6th edition, pages 222, 223, was found to more closely approximate that of glass rather than that of uncoated Lucite.

Example II.-55 parts by weight of allyl chloracrylate was heated with 3 parts by weight of benzoyl peroxide and 350 parts by weight of acetoneat a temperature of 60 C. for 4 hours. At this time, 300 parts of methanol were added to produce turbidity, and the resulting mixture was poured slowly, with stirring, into 1600 parts of methanol. The white voluminous precipitate thus formed was filtered and dried, and was soluble in acetone and chloroform and softened at 1l0125 ,C. It was a highly plastic gum at 140-150 C.

hardening with further heating.

A sheet of polymerized methyl methacrylate -drous oxalic acid, 116 grams (2.0 moles) of allyl alcohol, and 3.2 grams of p-toluene-sulfonic acid were heated together at l30 -l40 C. for 22 hours. The water and excess alcohol were then removed by slow distillation. The diallyl oxalate was then distilled at a temperature of 106-101 C. under a A sample of diallyl oxalate containing 5 percent by weight of benzoyl peroxide was heated at 80-85 C. for one hour at which time the viscous solution was poured into methyl alcohol to recover the fusible polymer. A solution containing 5.5 grams of the fusible polymer and 0.5 gram of benzoyl peroxide per 100 cc. of solution was applied to the surface of a sheet at 150 C. under a pressure of 1200 pounds per square inch for hours. The cured sheet possessed a hard, solvent-resistant surface.

Example IV.--A quantity of monomeric, ethyl ene glycol dicrotonate was heated with 5 percent by weight of benzoyl peroxide at 150 C. until the solution became viscous. The solution was then cooled to room temperature and introduced into an equal portion of acetone and the fusible polymer was precipitated with methyl alcohol as in Example I. A coating of a 5 percent solution of this polymer containing 0.5 percent benzoyl peroxide was applied to the surface of a polymer of methyl methacrylate copolymerized with suilicient allyl crotonate to render the product insoluble. After this coating was dried the coated polymer was placed in a mold and heated to a temperature of 150 C. for 2 hours, at a pressure of 1000 pounds per square inch. The article possessed a hard, solvent-resistant surface.

Example V.-Glycol dimethacrylate containing 1 percent benzoyl peroxide and 0.1 percent hydroquinone heated at 74 C. until the viscosity of the liquid was approximately doubled. The liquid was then treated with methyl alcohol as described in Example I, and a 5 percent yield of a white acetone soluble precipitate was produced.

A xylene solution containing 10 grams of this precipitate per 100 cc. of solution was applied to the surface of a sheet of a methyl methacrylate polymer as described in Example I, and a product having a hard, wear-resistant surface was thereby secured.

Example VI.A quantity of monomeric allyl crotonate was heated in a stream of air at a temperature of ISO-160 C. until the liquid began to get viscous. The liquid was then dissolved in acetone and the fusible polymer was precipitated with methyl alcohol in the manner described in Example I. The precipitated polymer was recovered as a white, gummy mass which dried to form a white, acetone soluble powder. A 5 percent solution of this powder containing 0.5 gram of benzoyl peroxide in xylene was applied to a sheet of polymeric methyl acrylate and cured in,

a mold at a pressure of 1000 pounds per square inch at a temperature of 140 C. for 2 hours. The resulting product possessed a hardened, solventresistant surface.

Example VII.--A sheet of cellulose acetate was coated with a film of nitrocellulose and then coated with fusible allyl methacrylate in the manner described in Example I, and a sheet having a hard, solvent-resistant surface was thereby secured.

Example VIII .-A quantity of diallyl phthalate was prepared by heating a mixture of allyl alcohol and phthalic anhydride, which contained allyl alcohol in an amount slightly in excess of the theoretical amount required for diallyl phthalate, to a temperature of -95 C., in-the presence of 2 percent paratoluenesulphonic acid for 15 hours. The mixture was washed with 0.1 N sodium hydroxide solution to remove acid and unreacted material and the diallyl phthalate was recovered by distillation at a pressure of 6 millimeters and a temperature of 170 C.

One part by weight of diallyl phthalate containing 5 percent benzoyl peroxide was heated at 90-95 C. for one-half hour and was then dissolved in two parts by weight of acetone. Methyl alcohol was added to the solution in an amount required to completely precipitate the polymer. This polymer was then redissolved to form a 10 percent solution in acetone which contained 1 percent benzoyl peroxide, and a sheet of polymerized methyl methacrylate was dipped into the solution. The dipped sheet was then heated at a temperature of 150 C. under a pressure or 1000 pounds per square inch for 4 hours. The resulting produce possessed a hardened, solvent-resisting surface..

Example IX.A quantity of ethyl allyl maleate was heated with one percent benzoyl peroxide at C. for 15 minutes, when the product began to grow viscous heating was then discontinued and sufllcient methyl alcohol was added to completely precipitate the polymer. The polymer was then redissolved in acetone to form a 5 percent solution thereof which contained 0.5 percent of benzoyl peroxide. This solution was a lied to a sheet of polymeric methyl methacrylate and the sheet was heated in a mold at C. under a pressure of 1200 pounds per square; inch for 6 hours, whereby a product having a hardened, solvent-resistant surface was secured.

.Example X .-l5 cc. of the xylene solution of the allyl methacrylate polymer described in-Example I; was applied to each square foot of surface of a Example XI.A xylene solution of glycol dimethacrylate prepared as described in Example V was applied as in Example I to the surface of a copolymer formed by copolymerizing 50 parts of diallyl maleate and 50 parts of methyl methacrylate and the coated product was dried and cured as described as in Example I. A

Although the present invention has been described and claimed with reference to the specific details of certain embodiments thereof, it is not intended that such details shall be regarded as limitations upon the scope of the invention except insofar as included in the accompanying claims. This application is a continuation-in-part of our copending applications Serial No. 257,135, filed Feb. 18, l939,'and Serial No. 302,562, filed Nov. 2, 1939.

We claim:

1. An artificial glass which comprises a transparent rigid thermoplastic resin sheet which is surfaced with a film of a substantially infusible and insoluble polymer of an ester containing at least two unsaturated groups derived from an acid of the group consisting of acrylic and alpha substituted acrylic acids, said film being of a thickness not substantially greater than 0.002- inch.

2. An artificial glass which comprises a transparent rigid thermoplastic resin sheet which is surfaced with a film of a substantially lnfusible and insoluble polymer of an ester containing at least two unsaturated groups derived from anacid of the roup consisting of acrylic and alpha substituted acrylic acids, the surface thereof being characterized by the fact that a point weighted to make a permanent mark and moved across the surface produces an elastic scratch.

3. The product of claim 1 in which the base is polymerized methyl methacrylate.

4. The product of claim 1 in which the surface ester is glycol dimethacrylate.

5. The product of claim 1 in which the ester is an ester of a glycol and an acid of the group consisting of acrylic and alpha substituted acrylic acids.

IRVING E. MUSKAT. MAXWELL A. POLLACK. FRANKLIN STRAIN. WILLIAM A. FRANTA. 

